Acrylic resins bonded to polystyrene



United States Patent ACRYLIC RESINS BONDED TO POLYSTYRENE Johan Bjorksten, Madison, Wis., Stuart 0. Fiedler, Cleveland, Ohio, and Luther L. Yaeger, Madison, Wis, assignors to American Motors Corporation, a corporation of Maryland i No Drawing. Application December 12, 1952, Serial No. 325,726

8 Claims. (Cl. 117--138.8)

This application relates to acrylic resins andmore particularly to such resins bonded to polystyrene.

Heretofore, synthetic resins applied to the surface of polystyrene articles have been found useful for providing polystyrene articles with improved surface characteristics such as improved abrasion resistance, improved optical properties, improved solvent resistance and the like. However, it has not been possible to secure sufficiently good bonds, that is sufficiently good adherency between such synthetic resins and polystyrene, and it has not been possible to provide such resins, and particularly acrylic resins, which could be applied to form a layer having the characteristics of a coating or laminate, which therefore would be integrally bonded to said polystyrene, and which could be removed at will on a commercially successful basis. This invention overcomes these disadvantages.

It is therefore an object of this invention to provide an acrylic resin or resins bonded to the surface of polystyrene by a bond at least as strong as the co-hesive bonds in the respective materials which can yet be removed discretely from the polystyrene at will by commercially successful processes. Another object is to accomplish this Without use of pressure or elevated temperature. Further objects will become apparent as the following detailed description proceeds.

The present invention represents an improvement over previous superior coatings for polystyrene disclosed in U. S. Patents 2,578,665, 2,578,683 and 2,578,770 and also.

disclosed in co-pending applications Serial No. 23,392 filed April 26, 1948, entitled Chemical Composition and Method, Serial No. 4,945 filed January 28, 1948, entitled Surface Treatment of Plastic Products, SerialNoQ 221,117

filed April 14, 1951, entitled Surface Treated Plastic Mate-f rials, and Serial No. 262,474 filed December 19, 1951,

entitled Coating Composition for Plastics.

This application is a continuation-in-part of said applications.

It has been found that in providing acrylic resin compositions adapted to provide acrylic resins adherent to the surface of polystyrene, it is highly desirable in commercial practice that the adhesivity for polystyrene be very great and be of such an order of magnitude that the forces of adhesivity in the bonding layers be greater than the forces of co-adhesivity in'either the acrylic resin or the polystyrene. It has also been found to be highly desirable in commercial practice to remove such acrylic resins from such polystyrene in order to permit the reclaiming of molded polystyrene articles which have been found to be defective only after having been provided a by these patents and applications have been made and marketed commercially for some time and several prob- Com- 2,801,936 Patented Aug. 6, 1957 ice . 2 lems have made themselves apparent in providing suitable coatings which satisfactorily fulfill all requirements of customers.

In particular, as disclosed in Patent 2,578,665, it is generally necessary to provide complex and delicately balanced solvent mixtures for polymers comprising ethylacrylate, methylacrylate, ethylmethacrylate, methylmeth: acrylate and co-polymers of these resins in order to provide satisfactorily adherent coatings for polystyrene.

It has been possible to provide on a commercial basis coatings comprising these polymers in balanced solvent mixtures prepared in accordance with disclosures of the applications of which this application is a continuation-inpart.

However, customers in certain cases desire to remove the coating after it has once been applied. This situation arises in the case of articles which are rejected as being poor. moldings or for mechanical reasons and from which customers desire to reclaim the resin of which these articles have been made. However, as mentioned in Patent 2,578,665 and in the applications of which this application is a continuation-in-part, it is extremely difiicult to remove polymers of ethyl and methyl esters of acrylic and methacrylic acids on polystyrene deposited from the solvent mixtures of these several inventions because the solvent resistance of the coating is high and the bond is extremely strong so that neitherchemical nor mechanical methods suffice. Several such customers have complained and other potential customers have refused to buy simply because they could not remove layers of these polymers from polystyrene articles rejected on inspection after being coated, from which they desired to reclaim the polystyrene resin.

It has therefore been desirable to provide resin coating compositions which such customers can use on polystyrene to provide an extremely adherent and therefore highly satisfactory coating but yet which could be removed sim ply and easily by customers.

It may be thought that it might be possible for the customer to remove polymers of ethyl and methyl acrylate and ethyl and methyl methacrylate from polystyrene by the use of the same solvent compositions or at least the same type of solvent composition used to deposit such polymers on polystyrene but in practice this has not worked out simply because such mixtures must be complex and delicately balanced and it has not been found possible to provide customers with such complex and delicately balanced compositions, especially for use in dissolving a polymer off an article rather than for depositing such polymer on the article. For example, it has not been possible to provide any single complex solvent composition which would remove all coatings prepared with polymers of ethyl and methyl acrylate and ethyl and methyl methacrylate and therefore it has been considered to provide customers with a plurality of such compositions but this has not been found practicable because the technological knowledge required of employees of such customers has been found to be inadequate for choosing the right composition to remove any specific coating. Also, solvent compositions which have been found suitw able for depositing such polymers have been found useless for removing the same polymer because the relative rates of evaporation of the members of the composition are such that the compositions do not function for the removal operation.

All such disadvantages have been overcome by providing coating compositions adapted to be applied to polystyrene and halogenated polystyrene which comprise esters of acrylic acid or methacrylic acid or both, halog'enated or unhalogenated, which contain at least 3 carbon atoms in the alkyl radical. It is true of course that not all of such esters, the higher esters of acrylic and polystyrene but which may vary in their surface properties to fit various needs of customers, and yet all of which can be removed by any one of several simple solvents or solvent compositions, the most suitable generally being methacrylic acids or copolymers thereof, have been found 6 a matter of choice based on the cost involved, which is suitable for every possible coatingpurpose by .such cusof course a highly important factor, a salient critical factomers since coatings. prepared with polymers such as tor to one engaged in manufacture and sale.

n-amyl methacrylate, n-hexyl methacrylate and-even n- Adherence of a polymer to a polystyrene sample is butylacrylate, and particularly lauryl methacrylate are determined by pressing firmly against the layer of polyverysoft and even tacky, but coatings of this type may mer a strip of pressure-sensitive tape extending entirely be utilized for adhesives and for trapping insects and a across the surface of the sample. One end of thispresvaluable application appears to be the use of such coatsure-sensitive tape is then lifted substantially --at right ings for dust-removal devices. The use of such coatings angles to the surface of the sample and visual observation in dust removal is of little commercial importancewith is used to determine whether the coating is thereby rerespect to large scale plant size installation because of moved from the polystyrene.

expense but may be highly adaptable to certain applica- Adherence of the coating for polystyrene is also detertions in connection with some scientific instruments, parmined by a scratch test, in which a standard phonograph ticularly those in connection with which it is undesirable needle carried upon the end of a horizontally pivoted to utilize an electrostatic field. The particularly great arm, is let down upon the coated surface of the sample value of the esters containing more than 3 carbon atoms approximately /2 inch from one edge and the sample lies in the fact that the customer may easily remove all is then slidably withdrawn from under the needle. A

such coatings by means of any one of several simple load of 1.5 lbs is maintained upon the needle. Nonsolvents or extremely simple solvent mixtures and this is adherency of the coating for polystyrene is observed by shown by Table 2 below. It may be observed from Table separation of the coating from the polystyrene face, ad-

2 that a very sharp dividing line exists between the esters jacent the scratch thus produced and the test is recorded containing only 1 or 2 carbon atoms on the one hand and as negative if any separation whatsoever is observed.

the esters containing 3 or more carbon atoms on the It is shown quite well by Table 1, which showsvarious other hand, all of the latter esters being soluble in such suitable coating compositions adapted to provide adsimple solvents and solvent compositions as are shown herent coatings with polystyrene, comprising certain esters in Table 2 whereas the ethyl and methyl esters and their of halogenated and unhalogenated acrylic and methacrylic copolymers are not soluble in these compositions. It is acids, that a wide variety of solvents and solvent mixtures thus made possible by this invention to provide customers may be used, in order to provide a coating composition with coatings having uniformly excellent adherence for adapted to not attack the surface of a polystyrene article:

Table 1 Example 1 2 3 4 5 6 -7 8 9 10 Monomer or Monomers from which methyl ethyl n-propyl lso-propyl n-butyl isobutyl tbutyl ehloro-nn-hexyl dichloro Polymer formed acrylate acrylate acrylate acrylate acrylate acrylate acrylate butyl acrylatecyclohexyl aorylate aerylate Type of Application for which formulation Spray Spray Dip Spray Spray Spray Spray Spray Spray Spray is suitable or Dip polymer 10 20 15 15 7. 1 10 10 10 10 10 acetone 42.9 35.5 30

methylethyl ketone methylbutyl ketone.

methyl isobntyl ketonem dlpropyl ketone dlbutyl ketone cyclohexanone.-

ether-1101-.--

n-propanoL isopropanoL.

isobutanoL-.-

tertiary butanol.

amyl alcohoL iso-arnyl alcohol hexanol ethylene glycol monobutyl ether ethylene glycol monomethyl ether acetate. ethylene glycol monethyl ether acetate ethylene dichloride chloroform esoi ose Table J.-"-C0ntinued Example 11 12 13 14 15 16 17 18 19 Monomer or Monomers from which n-octyl zethyl cyclohexyl methyl ethyl n-propyl isopropyl n-butyl isobutyl Polymer formed acrylate hexyl aerylate methacrymethacrymethacrymethacrymethacrymethacryacrylate late late late late late late Type of Application for which Spray Dip Spray Spray Spray Dip pr y p y p y formulation ls suitable dipropyl ketone dibutyl ketone ey clohexanone.

methanolethanol.

n-propanol isopropanoL- n-butanoltertiary butanolamyl alcohol"... iso-amyl alcohol. hexanol methyl acetate butyl acetate.- amyl acetate.

nitropropane cyclohexane toluene diacetone alcohol ethylene glycol mon'omethyl ether ethylene glycol monoethyl etheL ethylene glycol monobutyl ether ethylene glycol monomethyl ether acetate ethylene glycol monoethyl ether a etat c e ethylenediohloridech1or0form v Example .Q 2o 21 22 2a 24 25 2e 27 Monomer or Monomers from which Polymer t-butyl di-ehloi'o lso-amyl n-hexyl cyclo-hexyl n-octyl Z-ethyllauryl formed 7 methabutyl methamethamethamethahexyl methacrylate methacrylate erylate erylate crylate methaerylate crylate crylate Typet (g1 Application for which formulation is Spray Spray Dip Spray Dip Spray Spray Spray em a e l a polymer acetone methylethyl ketone methylbutyl ketone methyl isobutyl ketone. dipropyl ketone methyl lactate ethyl lactate. butyl lactate amyl lactate nltromethane. nitroethane.-- nitropropane. cyclohexane n-heptanekerosenenaphtha n-hexonp benzene toluene Tabla Ii -Continued Example. 20' 21 22 23 24 25 26 27 Monomer or Monomers frornwhich Polymer t-butyl di-chloroiso-amyl n-hexyl cyclo-hexyl n-octyl 2-ethyllauryl formed methabutyl methamethemethamethahexyl methac'rylate methacrylate crylate crylate crylate methacrylate crylate crylate Spray Spray Dip Spray Dip Spray Spray Spray Type of Application for which formulation is suitable diacetone alcohol ethylene glycol monomethyl ether ethylene glycol monoethyl etherethylene glycol monobutyl ether ethylene glycol monomethyl ether acetateethylene glycol monethyl ether acetate.

ethylene dichloride chloroform r Example; 28 29 30 31 32 33 Monomer or Monomers from which Polymer formed methyl n-butyl acryl'ate methyl 'methan-butyl n-hexyl isobutyl n-butyl methacrylate crylate methacrylate methacrylate acrylate and acrylate and and ethyl and cyclohexyl and iso-octyl u y cyclohexyl acrylate methyl methacrylate acrylate methacrylate methacrylate acrylate Type of Application for which formulation is suitable- Spray Dip Spray Spray Spray polymer acetone methylethyl ketone methylbutyl ketone. methyl isobutyl ketonedlpropyl ketone dlbutyl ketone cyclohexan0ne methanol. ethanol.

methyl acetate butyl acetatediacetone alcohol ethylene glycol monomethyl etherethylene glycol monoethyl ether. ethylene glycol monobutyl other ethylene glycol monomethyl ether acetate ethylene glycol monoethyl ether acetate.. ethylene dichloride chloroform Such attack is represented by dissolving of the polysystematic form by chemical classification, the groupings and their proportions according to which a suitable solstyrene surface and by swelling of the polystyrene at and adjacent to this surface. It is also represented by blushing vent mixture may be provided. of the polystyrene and it is probably most often represented, especially in polystyrene containing internal strains fl Subsequently it has been found that numerous addi- 1 tional solvent compositions other than those falling within of especially great magnitude, by crazing and even crackthe described grouping are highly suitable and this is ing of the polystyrene surface. Such coating compositions ,Qespecially true for the esters containing more than 3 carare adapted to deposit on the surface of the polystyrene -bon atoms. It has not been possible to establish any a coating consisting entirely of the acrylate, or methaff 'ichemical grouping or classification in terms of chemical crylate or copolymer by virtue of the volatility characternomenclature to describe such solvent mixture and if it istics of the solvent mixture and by virtue of the simul- 'iwere possible it has become quite evident by now that taneous properties of adhesivity of the acrylate or methacrylate or copolymer for polystyrene surfaceslwhichis apparent only in the presence of a solvent liquid 'of' the type described.

Heretofore it has been attempted to set I forth in Markush form or ingeneric form or otherwise in some other any such description would be in the nature of a phase diagram, except that instead of the conventional 3 phases describe and it is further more apparent that in order to determine all the boundarylines and boundary surfaces for such a diagram a research program of several thousands or even tens of thousands of man hours would have to be instituted. It is believed similarly obvious to even the uninitiate that the situation could not possibly justify such a research program.

Table 2 which shows results obtainable with 4-inch by 4-inch by quarter-inch samples of injection molded polystyrene coated with each of the compositions shown in Table 1, concisely shows the inapplicability of the methyl and the ethyl esters of acrylic and methacrylic acid for the present invention due to their insolubility in simple solvent compositions such as 20% acetone and 80% methanol, shown there, coupled with the corresponding solubility of every one of both the halogenated and unhalogenated esters of acrylic and methacrylic acids containing more than 3 carbon atoms:

Table 2 Solubility (Completely Miscible in All Proportions) Adherence to Polystyrene Example Pressure Sensitive Scratch Test Tape Test TA B o Adherent Adherent. o... o.

yes-...

A-Ethylene glycol monomethyl ether. 13-20% acetone, 80% methanol.

90% n butanol+l0% methyl ethyl ketone.

It is shown also by Table 2 that the adhesivity or adherency of all such esters is generally at least excellent but it must be remembered that these results are conditioned upon the esters being dissolved in a solvent composition according to the invention and that such results cannot be obtained with solvents of the usual type disclosed in the prior art such as 100% ethanol or 100% acetone.

From the above description and the data shown in Tables 1 and 2 it may thus be seen and should be clearly understood that the invention relates to causing a layer of acrylic synthetic resin to adhere to at least one surface of a polymer formed from at least one monomer having the chemical formula wherein X is -H, -Cl or -Br and wherein :15 represents phenyl which may be halogenated. Such polymer may be copolymerized with other materials particularly such as butadiene and acrylonitrile, copolymers of this sort being only those which comprise at least some proportion of the polymer according tosaid formula.

It should also be apparent and should be understood that said acrylic synthetic resin is a polymer formed from at least one monomer having the following chemical formula:

wherein R1 is H or CH3 and R is a saturated aliphatic radical, which may be halogenated, containing at least 3 carbon atoms and that every monomer included within the scope of this definition is included within the invention and is operable for the invention so far as it has been possible to determine within the reasonable scope of chemical research. Diiferences have been observed between the acrylate monomers and methacrylate polymers, that is, diiferences have been observed between those compounds wherein R1 is -H and those compounds wherein R1 is CH3, but such differences have not been observed to have applicability to the present invention. It has been particularly determined by careful research that. polymers of the ethyl and methyl esters of halogenated and unhalogenated acrylic and methacrylic acids are not operable for the invention as is clearly shown by the above disclosure, and it is thus not possible to consider them equivalents of the compounds included within said definition. 1

It may of course be possible to include other materials, particularly other polymers such as those which undergo vinyl polymerization, including vinylcarboxylates such as vinyl acetate, vinyl b utyrate and thelike, styrenes and halogenated styrene, ethylene, fluorinated or chlorinated ethylene, acrylonitrile, butadiene and the like in a coating composition and thus obtain suitable coating compositions for polystyrene. It may also be feasible to include in the composition polyfunctional compounds or compounds containing non-conjugated ethylenic groups which serve as cross-linkers but generally speaking it has been found preferable to limit the coating compositions according to this invention to those falling within the above definition.

Although the scope of the polymeric ingredient in the coating compositions according to the invention has been carefully set forth above and the nature of the solvent which is necessary for the coating composition of the invention has been set forth above, it may be further mentioned that the coating compositions according to the invention include a polymeric component and a non-polymeric solvent component and it has been found critically necessary that they include both of said components and that each of said components fall within the above mentioned definitions. It has furthermore been found preferable that the solvent compositions according to the invention not include any other substance such as, particularly, a plasticizer.

It should be particularly pointed out that the solvent compositions of the invention and the coatings applied to polystyrene and its homologues according to the invention are prepared without incurring the disadvantages of causing the coating to undergo either a heating step or a pressing step. That is, a slick, smooth, optically suitable coating is applied, utilizing a composition which neither balls up, chips, sags, runs nor does any of the other myriad of things that inferior coating compositions have a tendency to do and this result is accomplished wit out at any time having to press the coated article between glass or metal platens in a press, without having to subject the coated article to any curing step which may require an oven, and in general without incurring any steps other than the application of the coating and the subsequent air drying of the coating.

This is a remarkable result as most methods of the prior art have required application of either heat or pressure and usually have required the application of both in order to obtain suitable coatings. The difference from a technological point of view is highly significant; it may best be measured by the respective costs which are not even remotely comparable.

Despite the fact that it is not necessary, according to the process of this invention, to subject the coated article to heat in order to provide the coating of the invention, the coated article may be subjected to curing temperatures, if the user desires to do this, without stepping outside the scope of the invention since in some circumstances such heating, though not necessary, may accelerate the air-drying step or may in some other manner suit better the needs of the user and such heating in no way destroys or makes less effective the coating of the invention so long of course as the heating is restricted to temperatures below the softening point of either of the above defined polymers.

It may thus be seen that the invention is broad in scope and should not be limited excepting by the claims.

Having thus disclosed our invention, we claim:

1. An article comprising polymerized styrene having adherent thereto a layer of a polymer formed from at least one monomer having the following chemical formula:

consisting of saturated aliphatic radicals and halides thereof which contain at least three carbon atoms.

12 The article of claim 1 wherein R is C3H'z. The article of claim 1 wherein R is C-1H9. The article of claim 1 wherein R is C5H11. The article of claim 1 wherein R is CsH11. The article of claim 1 wherein R contains eight carbon atoms.

7. An article comprising a polymer formed from a monomeric material comprising styrene provided 011 at least part of a surface thereof with an adherent layer of a polymer formed from at least one monomer having the following chemical formula:

wherein R1 is selected from the group consisting of -I-I and -CH3 and R is a radical selected from the group consisting of saturated aliphatic radicals and halides thereof which contain at least three carbon atoms.

8. The article of claim 7 wherein R1 is --H.

References Cited in the file of this patent UNITED STATES PATENTS Graves Apr. 15, 1941 2,292,393 Mitchell Aug. 11, 1942 2,407,668 Leatherman Sept. 17, 1948 OTHER REFERENCES 

1.AN ARTICLE COMPRISING POLYMERIZED STYRENE HAVING ADHERENT THERETO A LAYER OF A POLYMER FORMED FROM AT LEAST ONE MONOMER HAVING THE FOLLOWING CHENICAL FORMULA: 